Surface-active polymers derived from naturally occurring polysaccharides have applications in numerous areas, including detergents, cosmetic, and pharmaceutical products. In these products, the role of the surfactant is to lower the interfacial surface tension between dissimilar phases therefore improving compatibility of the phases. Surfactants can act as emulsifiers, stabilizers, wetting aid and also assist in cleaning processes.
In the cleaning products industry, soaps based on natural oils were very common several decades ago. With the advent of high performance detergents, the use of soaps derived from bio-based oils has declined considerably. The newer detergents are often non-biodegradable and can cause serious environmental problems. See for example, U.S Environmental Protection Agency, Nonylphenol (NP) and Nonylphenol ethoxylates (NPEs) Action Plan, RIN 2070-ZA09, 2010; Hoponick, Nonylphenol Ethoxylates: A Safer Alternative Exists to this Toxic Cleaning Agent. Sierra Club, 2005; and European Union. 4-Nonylphenol (branched) and Nonylphenol Risk Assessment Report. Institute for Health and Consumer Protection, European Chemical Bureau, Vol. 10, 2002.
With the goal of producing surface-active compounds from bio-based feedstock, several synthetic strategies have been reported. See for example, Stevens C. V et al., Polymeric Surfactants Based on Inulin, a Polysaccharide extracted from Chicory: Synthesis and Interfacial Properties, Biomacromolecules, Volume: 2 (4), pp 1256-1259, 2001; Yuping Wei et al., Amphiphilic cellulose: Surface activity and aqueous self-assembly into nano-sized polymeric micelles, Reactive & Functional Polymers 68, pp 981-989, 2008; Tianhong Zhang et al., Novel Polysaccharide Surfactants: Synthesis of Model: Compounds and Dextran-Based Surfactants and Dextran-Based Surfactants, Macromolecules, 27 (25), pp. 7302-7308, 1994; Pan Hong et al., Surface properties and synthesis of the cellulose-based amphoteric polymeric surfactant, Carbohydrate Polymers 69, pp. 625-630, 2007; and Alain Durand et al., Neutral amphiphilic polysaccharides: chemical structure and emulsifying properties, Colloid. Polym. Sci., 284: 536-545, 2006.
Polysaccharides are typically a common starting material for these surfactants, because they represent the most abundantly available bio-based, renewable feedstock in the world. Typically, polysaccharides have to be modified by a variety of synthetic chemical methods to yield surface-active properties. Several methods are available for the preparation of these polysaccharide derivatives. Some common derivatives include various alkyl ether derivatives (carboxymethyl cellulose, hydroxyethyl cellulose (U.S. Pat. No. 3,498,971 issued Mar. 3, 1970 to Blaga et al.), hydroxypropyl cellulose), polysaccharides modified with amphiphilic hydrocarbons, and glucose ethers as exemplified by U.S. Pat. No, 3,574,188 issued Apr. 6, 1971 to Takehara et al., U.S. Pat. No. 6,620,295 issued Sep. 16, 2003 to Shannon et al., and U.S. Pat. No. 2,974,134 issued Mar. 7, 1961 to Pollitzer, respectively.
In all of these cases, water-soluble polysaccharides are hydrophobically modified to yield amphiphilic molecules. Unfortunately, in some cases, the modifications require harsh reaction conditions that commonly lead to partial or substantial degradation of the polysaccharide. To date, the bulk of the research reported has been on either converting water-soluble polysaccharides into surface-active agents by attaching hydrophobic entities or multiple step conversions of water insoluble polysaccharides into soluble surfactants. It is therefore desirable to employ synthetic strategies that involve milder conditions (to preserve structural integrity) to yield amphiphilic products that are efficient surfactants.
Due to toxicity and environmental concerns, the use of nonylphenol ethoxylates is being phased out in several countries across the globe. Therefore, there is a need to create anew class of effective surfactants that can serve as drop-in replacements for NPEs.